1. Field of the Invention
The invention relates to communication systems and, more particularly to the creation, maintenance, use and deletion of virtual channels in a network environment.
2. Description of Related Art
Modern data networks trace their historical origins to telephone switching networks. Telephone switching networks set up connections between an originating caller and a called subscriber selected by dialing the called subscriber's telephone number.
Digital networks are known which permit information packets to be routed from a source to a destination without the necessity for a hardwired connection between the calling subscriber and the destination subscriber. Packets are routed over links between nodes of a network. Rather than a physical connection, a virtual connection, sometimes called a virtual channel or virtual circuit is defined between the source of the packet and its destination. A virtual circuit gives the appearance of maintaining a hardwire connection, but utilizes the resources of the connection only when data need to be sent. This permits the link to be shared by other virtual circuits and improves the efficiency and throughput of the links of the network.
One form of modern high speed network uses a set of standards collectively termed asynchronous transfer mode (ATM). The basic data element used by these networks is a cell, which is a sequence of 53 bytes of which the first 5 are the header and the other 48 are the cell payload. To allow very high data rates (in the hundreds of megabytes per second and above) the switching time of a cell in every switch or node along the route through the network must be minimal. ATM networks achieve this by way of a virtual channel mechanism which requires a set-up phase before the actual data stream can be transported from source to destination. The notion of a virtual path is defined in the ATM standard. Each virtual path "contains" 2.sup.16 (65,536) virtual circuits. Supporting virtual path requires significant additions to the ATM switch hardware. Consequently, many switches only support virtual circuits; they do not support virtual paths.
The Problems
It would be desirable to have an efficient mechanism for quickly allocating multiple connections. Further, it would be desirable to reduce the table size required for network switches to support large numbers of virtual circuits. It would further be desirable to implement multiple virtual channels set-up while maintaining compatibility with current switches but nevertheless supporting heterogeneity in switches in a network. It would further be desirable to be able to route multiple virtual circuits over different paths. It would also be desirable to support dynamic aggregation of individual virtual circuits into larger entities. It would also be desired to permit enhanced resource sharing across connections of a network. It would further be desirable to have techniques for handling ATM cell interleaving problems in a multi-sender multi-cast. It would also be desirable to have efficient support for fast connection establishment. It would further be desirable to improve the efficiency with which "keep-alive" and "refresh" packets are sent through the network.